Electronic component generates heat and the heat needs to be dissipated efficiently for the device to function properly. A common expedient for this purpose is to transfer heat from electronic component (FIG. 1-5) to a heat spreader (FIG. 1-2) and heat sink (FIG. 1-1) through an integrated thermal path, which was established by attaching a heat spreader directly on the electronic component using thermally conductive interface materials (FIG. 1-4, 3). Effectiveness of heat dissipation is dominated by thermal conductivity and mechanical integrity of the interface materials.
Due to the relentless pursuit of computing performance and functionality, improving heat dissipation becomes one of the central issues. The recent trend in microprocessor architecture has been to increase the number of transistors, shrink processor size, and increase clock speeds in order to meet the market demand. As a result, the high-end microelectronic components are experiencing ever growing total power dissipation and heat fluxes, which increase the demand for effective means of heat dissipation.
Thermal interface material plays a key role in improving thermal dissipation efficacy. Thermal conductivity efficiency is disproportional to the nominal average thickness of thermal interface as illustrated in FIG. 1. Along with material thermal conductivity improvement, shorten thermal dissipation path across the thermal interface material linearly reduce the thermal resistance, but at a price of increasing stress introduced by thermal mismatch between silicone electronic component and heat spreader. Low viscosity and low modulus of thermally conductive materials is prominent to the reliability of electronic products, such as single chip module (SCM) and multichip module (MCM) as shown in FIGS. 1 and 2.
Thermal interface material is conventionally classified into following categories: sheet, grease, adhesive and gel. EP2532723A1 disclosed a formulation of polyacrylic based thermal sheet with rigid mechanical property, which yields non-compliant property. Thermal grease is prepared by mixing a silicone oil or polyolefin oil (U.S. Pat. No. 6,114,429, U.S. Pat. No. 5,591,789) with thermally conductive fillers. Poor cohesion, a parasitic disadvantage of thermal grease, results in “pump out” issue and explains its incapability as a conductive media for the organic packaging application. Thermal adhesives proposed in US 20120279697A1 uses polyester as polymeric liquid matrix, which produces strong interfacial adhesion with high rigidity, lacking of flexibility to accommodate mismatched thermal expansion introduced mechanical stress, especially associated to an interface with a nominal size of less than 250 um.
WO2004072181 proposed a range of formulations for silicone thermally conductive gels. However, the thermal conductivity claimed in the invention fall into the range of 3.5-4.2 W/mK with no consideration about thermal particle size and volume percentage selection.
In general, high thermally conductive filler loading is needed for high thermal conductivity. Thermal conductivity of commercial available conductive gel ranges from 1-4.5 W/m·K, and thermal gel with thermal conductivity greater than 3.5 W/mK tends to be too thick to satisfy thermal interface bonding application with nominal gap size of 250 um and below.